JSON output for test listing

[MatthewMckee4]

Support JSON output when listing discovered tests, for programmatic consumption:

karva test --dry-run --format json
karva test --dry-run --format json-pretty

This would output structured test metadata (name, module, tags, parameters, file path, line number) that other tools can consume for building test dashboards, selecting tests, or integrating with IDEs.

See: https://nexte.st/docs/listing/